Combine red lentils, chopped onion, sage and water in a large frying pan and bring to boil on medium heat. Then reduce heat and continue stirring for 10-15 mins or until all the water is absorbed.
At this point, the lentil mixture is about half done. You will want to end up with a fairly thick mixture in the end. If it is watery at all your pie will be mushy.
Preheat your oven to 400.
Behold my ghetto cooking pan! I'm actually quite proud of it, it's an old take out tin that I have reused a million times for different recipes. Who needs fancy pans? Anyways, pour some oil in the pan
Once the lentil mixture is thick enough, put in 2/3 of your cheese, salt and pepper and stir it up. I used marble and it got all stringy and gooey and lovely. At this stage I admittedly got excited.
Pour the mixture in your cooking pan and add the remaining cheese on top and toss 'er in the oven.
Bake for 20-30 min, until it becomes golden brown/awesome on top. I will warn you that when you take it out it will smell amazing. You will want to eat it. Resist this urge and let it cool for 10 min
Serve and enjoy! Mine ended up being a bit mushier than I would have liked. Next time I will have to cook it a bit longer in the frying pan. It was still super delicious though!